(1) Field of the Invention
The present invention generally relates to an electroytic capacitor comprising an anode foil, a cathode foil and an electroytic paper impreganted with electrolyte which paper is interposed between these foils. In its particular aspects, the present invention relates to improvements in proportion defective caused by short circuit between these foils, impedance property, impregnation ability of electrolyte or the like.
(2) Description of the Prior Art
Generally, an electrolytic capacitor, particularly an aluminum electrolytic capacitor, is produced in following process. An electrolytic paper is interposed between an anode foil and a cathode foil, and they are winded up. Succeedingly, liquid electrolyte is penetrated into them, and finally their ends are sealed. The liquid electrolyte for this capacitor is the solution of boric acid or adipic acid soluted is penetrated into the capacitor element from both its ends.
In the above mentioned conventional aluminum electrolytic capacitor, the electrolyte is penetrated in the electrolytic paper, so that its impedance property is poor. Further, this electrolytic paper tends to easily worsen during a long use. In order to avoid the generation of such demerits, the value of resistance of the electrolyte is decreased, thickness or density of the electrolytic paper is decreased, and/or commonly used wood craft pulp for the electrolytic paper is replaced by the particular material such as a manila hemp pulp, an esparto pulp or the like.
However, these treatments also cause another problems. Decreasing the resistance value of the electrolyte causes the corrosion of aluminum foil. Decreasing the thickness or density of the electrolytic paper increases the number of defects owing to short circuit when the paper is rolled up to form the capacitor. Even if the short circuit is not generated at the rolling up step, the product in its market will be often troubled on account of the short circuit caused in the electrolytic paper.
As typical prior arts of the electrolytic capacitor, Japanese Patent Application Publications No. Sho. 59-32121 and No. Sho. 56-131922 have been known. In No. Sho. 59-32121, the object of this invention is to increase the impregnating speed of electrolyte and uniform the impregnation. Therefore, this invention provides one composition comprising a single electrolytic paper formed with the recessed grooves in the same way as the above. The depth of each grooves in the range of 1/4 to 3/4 of the thickness of the electrolytic paper.
In No. Sho. 56-131922, the object of this invention is to perform effectively the impregnation of electrolyte even when the rolled dimension of the capacitor is relatively large, and thus this invention provides an electrolytic capacitor characterized by forming transversely extending printed sections in at least one of an anode foil and a separating paper.
The above two prior arts are only effective to improve the impregnating speed of electrolyte. These inventions do not suggest any intention or effectiveness to improve the proportion defective depending on short circuit and the impedance property.
According to these inventions, the thickness of the electrolytic paper formed with the grooves (printed sections) is almost equivalent to that of a non-treated electrolytic paper. Or otherwise, the thickness of the treated paper is relatively thick. Even if the treated paper is scarcely thicker than the non-treated paper, the treated paper will return to the initial thickness in a short time. Consequently, these prior arts do not relate to the improvements in the proportion defective on account of short circuit and the impedance property.
General discussion on the relation between the proportion defective owing to short circuit and the impedance property is as follows.
In order to decrease the proportion defective, skilled artisan makes the electrolytic paper to be thick or high density. If the paper is kept at the same density, the value of CSF (Canadian Standard Freeness), referred to JIS P8121, which indicates the smashed degree of pulp as a raw mateial for the paper is also decreased.
With respect to the impedance property, the impedance property is worsened as a simple equation when the thickness is increased and worsened as a quadratic equation when the density is increased. On the otheer hand, the impedance property is not affected by the value of CSF. Accordingly, in order to improve the impedance property, the electrolytic paper should be thin and low density on the contrary to the improvement of proportion defective owing to short circuit.
In order to improve both the proportion defective and the impedance property at the same occasion, it is preferable to decrease the impedance property is not affected by the value of CSF. Thus it is ideal to make a low density electrolytic paper by using the material with the small value of the paper is always increased as the value of CSF. However, when the paper is produced by using the pulp mainly consisting of a natural cellulose such as a commonly used craft pulp, an isparto pulp, or the like, the density of the paper is always increased as the value of CSF is decreased. If the paper with the same thickness is propuced by the identical paper manufacturing machine, the value of CSF of the high density paper is smaller than that of the low density paper. Accordingly, the value of CSF is increased when the low density paper is used to improve the impedance property of the electrolytic capacitor. This causes to increased the proportion defective due to short circuit. On the other hand, in the case of the paper having smaller value of CSF, the paper density is high and therefore the impedance property is further worsened.
As a result, both the propertion defective and the impedance property could not be effectively improved at the same occasion.
(3) Object of the Invention
With these problems in mind, it is an object of the present invention to provide an elective owing to short circuit and impedance property.
The other object of the present invention is to provide an electrolytic capacitor which can be impregnated with an electrolyte for a short time.